Our study to determine the mechanism of muscle contraction will concentrate upon separating sarcomere motion from motion at the ends of the muscle, the former being greatly influenced by tendon compliance. In studying this we will make use of optical diffraction techniques. Feedback will be used to control sarcomere motion. Stiffness measurements based upon the speed of propagation of small mechanical disturbances, will be used as a measure of cross-bridge interaction during isotonic shortening.